MINOR: log: Remove log-error-via-logformat option

This option will be replaced by a "error-log-format" that enables to use
a dedicated log-format for connection error messages instead of the
regular log-format (in which most of the fields would be invalid in such
a case).
The "log-error-via-logformat" mechanism will then be replaced by a test
on the presence of such an error log format or not. If a format is
defined, it is used for connection error messages, otherwise the legacy
error log format is used.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 0760ac8..428339a 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -9041,23 +9041,6 @@
              logging.
 
 
-option log-error-via-logformat
-no option log-error-via-logformat
-  Enable or disable dedicated connection error logging.
-  May be used in sections :   defaults | frontend | listen | backend
-                                 yes   |    yes   |   yes  |   no
-  Arguments : none
-
-  In case of connection error, if the option is disabled, a log line following
-  the format described in section 8.2.6, the legacy format, will be emitted.
-  Otherwise, a log line following the configured log-format for the listener
-  will be emitted. The error code and the corresponding message found in the
-  error log can be added to a log-format thanks to the "fc_conn_err" and
-  "fc_conn_err_str" sample fetches.
-
-  See also : "option httpslog" and section 8 about logging.
-
-
 option mysql-check [ user <username> [ { post-41 | pre-41 } ] ]
   Use MySQL health checks for server testing
   May be used in sections :   defaults | frontend | listen | backend
diff --git a/src/proxy.c b/src/proxy.c
index 2642b44..16da542 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -72,7 +72,6 @@
 	{ "http-ignore-probes", PR_O_IGNORE_PRB, PR_CAP_FE, 0, PR_MODE_HTTP },
 	{ "prefer-last-server", PR_O_PREF_LAST,  PR_CAP_BE, 0, PR_MODE_HTTP },
 	{ "logasap",      PR_O_LOGASAP,    PR_CAP_FE, 0, 0 },
-	{ "log-error-via-logformat", PR_O_ERR_LOGFMT, PR_CAP_FE, 0, 0 },
 	{ "nolinger",     PR_O_TCP_NOLING, PR_CAP_FE | PR_CAP_BE, 0, 0 },
 	{ "persist",      PR_O_PERSIST,    PR_CAP_BE, 0, 0 },
 	{ "srvtcpka",     PR_O_TCP_SRV_KA, PR_CAP_BE, 0, 0 },